Dealing with Varroa
Varroa has been a serious problem for bees in the UK for 20 years after it was imported from abroad. The varroa mite lives off the bees as a parasite and breeds in the cell where our bees pupate. As well as causing weakness in the bees by their parasitic action, they also spread disease – particularly deformed wing virus. A large varroa population will probably be fatal to your bees so treatment is needed. Integrated Pest Management is the order of the day and the Fera book explains it quite clearly.
An open mesh floor (to let any varroa that fall off fall out), icing sugar dusting and drone brood removal are all useful to keep varroa numbers down however chemical treatments will almost always be needed. Although icing sugar dusting has lost favour over the past few years. Some of the early treatments such as Bayvarol and Apistan are now not always effective in many parts of the country as the mites have become immune to them so they should be used on a rotation basis only. Apivar containing an insecticide called Amitraz is now licenced although it is expected that immunity will develop to this over time as well. A thymol treatment is often recommended. Apiguard and Apilife Var are probably the most common (Be aware of the the similarity of the name with Apilife Var, is confusing). The best time to treat is in August, once the honey has been removed. The treatments can put the queen off lay so don’t be alarmed if this happens. An August treatment allows egg laying to resume fully in September when the winter bees will be produced and will ensure there is enough time to have the hive ready for winter.
For thymol treatments your mite board should be in position under your OMF (Open Mesh Floor) both to catch the varroa for counting as well as to keep the fumes in. Follow the instructions on the packet! Once treatment has concluded, the mite board can be removed again.
MAQS strips are also available as they have been licensed for the UK. These only need to be in the hive for a week and can be on when there is honey in the hive. So worth considering although they may be a little more expensive than other treatments. There are some reports of problems in the hive as a result, although these are small in numbers and thymol treatments can also be troublesome.
A second treatment of Oxalic Acid is used by many beekeepers. Oxalic Acid is dribbled onto the bees or vaporized and should be done when the bees are broodless or it will be ineffective. A swarm is a good candidate for this reason, so is treatment in the depths of winter – late December or early January – when there will be little if any brood. Again a mite board under the OMF will inform us if we have had a serious problem. Follow the instructions given by the supplier. LASI have instructions for fogging the bees with Oxalic Acid. You'll need the correct equipment including the mask (PPE) as the vapour is dangerous.
Deformed Wing Virus shows itself by nurse bees having little or no wings in the hive or by noticing bees walking away from the hive. Once you see a few bees with it, you may well have a serious problem. Use the Fera website for guidance about counting the mites. Icing sugar dusting may keep varroa numbers down for a little while. The most noticeable time for DWV is in July and onwards. The reason for this is that as brooding start to decline after the end of June there will be a larger proportion of varroa as varroa numbers continue to increase as the brooding decreases. The varroa numbers continue to rise and rise until the colony can collapse or not survive into the new season. Bees dying in the cells and a collapse in numbers is referred to as Parasitic Mite Syndrome.
At the end of the summer, it is important to get your colony as strong as possible for the winter so allowing an untreated varroa infestation to continue is just daft. Consider the cost of treating a colony – just a few pounds - compared to the cost of buying a replacement nuc. Some beekeepers try to not treat their colonies to keep things natural and I understand this philosophy. There is also work going on with regard to hygenic bees - ones that remove the varroa themselves - which would be the ideal. (Check out the Sussex University website (LASI) for information. My own personal opinion is that if you want to not treat for varroa, keep bees for a couple of years first before deciding and the expect considerable losses.